1. Field of the Invention
This invention relates to a refrigerating cycle, having a main line and a by-pass line, a compressor, a condenser in said main line downstream the compressor, an evaporator downstream said condenser, an accumulator between said evaporator and said compressor, at least one expansion valve means for adiabatically expanding a refrigerant, and refrigerant flow switching means for selectively supplying the refrigerant in a cooling mode to said condenser and in a heating mode to said by-pass line. The evaporator usually used for cooling purposes, on demand can be used for auxiliary heating instead.
In air conditioning systems for automobiles, an ordinary refrigerating cycle is used for cooling, while heated engine cooling water is used for heating purposes. However, with high-efficiency engines such as recently developed direct gasoline injection type engines, the heat content of the cooling water is far less than with conventional combustion engines, leading to the drawback that the heat content does suffice sufficiently for heating purposes, e.g. in wintertime.
2. Description of the Related Art
A known refrigerating cycle (U.S. Pat. No. 4,893,748), and as shown in FIG. 12, comprises a by-pass line 5 for high-pressure refrigerant gas discharged from a compressor 1 to flow into an evaporator 4 arranged inside a vehicle compartment but without passing through a condenser 2 arranged outside the compartment, so that a sensitive or sufficient amount of heat may be removed in the process of heat exchange by the evaporator 4 to be used for auxiliary heating. Said known refrigerating cycle comprises an expansion valve 3, a liquid tank for temporarily storing high-pressure refrigerant liquid, a check valve 7, a line switching valve 8 for directing the high-pressure refrigerant from the compressor 1 to the condenser 2 or the by-pass line 5, and a constant-differential-pressure regulating valve 9 acting as an expansion valve in the heating mode when the refrigerant is passing the by-pass line 5. Since in the known refrigerating cycle the refrigerant does not pass the liquid tank 10 in an auxiliary heating mode only a fixed amount of refrigerant is circulating in the heating mode. Consequently, the amount of the refrigerant cannot be controlled in accordance with load, etc. It is impossible to adapt the heating to such conditions. Furthermore, in case of high speed of the compressor 1 high pressure is acting in evaporator 4. As a consequence, it is necessary to have an evaporator 4 with increased pressure resistance resulting in extremely high manufacturing costs.
Further prior art is contained in U.S. Pat. No. 5,291,941, FR 27 20 982 A, FIG. 1, EP 0 895 884 A and in EP 0 916 914 A having an earlier time ranking.
It is an object of the invention to provide a refrigerating cycle of the kind as disclosed which allows to suitably adapt the heating function in the auxiliary heating mode to actual conditions and which leads to fair production and manufacturing costs. In particular, the refrigerating cycle should allow to control the amount of the circulating refrigerant in accordance with load, etc. and to eliminate the need to increase the pressure resistance of the evaporator for the auxiliary heating mode.
Said object is achieved by the refrigerating cycle according to the invention and with the feature combination contained in claim 1.
When the refrigerant is circulating through the by-pass line without passing through the condenser (auxiliary heating mode), the flow rate of the refrigerant is controlled by the accumulator such that the amount of the circulated refrigerant is controlled in accordance with load, etc. It is thus possible to provide heating suited to such conditions. The regulator controls the outlet pressure of the evaporator such that the refrigerant temperature can be maintained to ensure the heating capacity. The evaporator does not need to have an increased pressure resistance. This allows to construct and manufacture the refrigerating cycle at ordinary costs.
Small fluctuations of the outlet pressure of the evaporator or the inlet pressure of the regulator can be tolerated for a proper operation of the refrigerating cycle. This is achieved by keeping the inlet pressure at a fixed pressure value or higher or at a fixed pressure value or lower.
A regulator having a pressure limiting main valve responsive to the value of the inlet pressure and/or the outlet pressure of the evaporator limits the outlet pressure of the evaporator to a fixed level or around a fixed level. This can be made by either limiting the minimum pressure value and allowing smaller pressure variations to a higher pressure value or by limiting the maximum pressure and allowing smaller variations of the pressure to a lower pressure value. In any case, an ordinary design of the evaporator without increased pressure resistance can be used. The tolerated pressure variations, above the minimum pressure value or below the maximum pressure value are automatically controlled in the heating mode by the pressure controlling characteristic of said pressure limiting main valve.
A pressure range of about 0.2 to 1.5%, preferably about 0.4 to 1.0% above said minimum or below said maximum pressure value, respectively, are tolerable and will not cause undesirable high pressure load for the evaporator during the heating mode.
The actual prevailing outlet pressure of the evaporator is controlled by motions of the pressure limiting main valve between its open and closed states and by the natural throttling resistance in the fully opened valve. The control characteristics of the pressure limiting main valve depend mainly on the spring assembly used to bias the valve in closing direction. The pre-load of said spring assembly can be adjusted on demand. The diaphragm does not only transmit the force of the pressure uniformly onto the spring assembly but additionally seals the spring assembly and protects it from contact with the refrigerant. Preferably, said spring assembly is designed for a relatively long opening stroke of the valve with a relatively constant spring behaviour.
In order to avoid unstable operating conditions a leak passage with a small cross-sectional area in comparison with the cross-sectional area of the refrigerant line is detouring the regulator and directly interconnects the evaporator and the accumulator. Even in the fully closed state of the regulator the leak passage allows a delayed pressure exchange and a minimum refrigerant flow. In order to avoid an undesired influence of the regulator on the cooling mode an on-off valve allows to by-pass the regulator. Preferably, said on-off valve is a actuated corresponding with the refrigerant flow switching means when switching the refrigerating cycle into the cooling mode or into the auxiliary heating mode. For manufacturing purposes and in order to save mounting space the regulator and the on-off valve structurally can be united in a common valve block.
It can be particularly expedient to provide the regulator between a pressure control chamber and an outlet of the on-off valve, if the on-off valve is designed as a pilot-operated electromagnetic valve.